<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script  type="text/javascript" src="https://cdn.bootcdn.net/ajax/libs/jquery/1.10.0/jquery.js"></script>
    <script>
        $(function(){
            //alert("页面加载完成！");
            //alert($("button").length);
            alert( $( "<h1></h1>" ));
        });

    </script>
</head>
<body>
    <button>按钮1</button>
    <button>按钮2</button>
    <button>按钮3</button>
</body>
</html>